Temperature-responsive current control device



H. WEISS Oct. 25, 1966 v TEMPERATURE-RESPONSIVE CURRENT CONTROL DEVICE 2 Sheets-Sheet 1 Filed Dec. 11, 1964 LOAD FIG. 1

FIG. 2

Oct. 25, 1966 H. WEISS 3,281,749

TEMPERATURE-RESPONSIVE CURRENT CONTROL DEVICE Filed Dec. 11, 1964 2 Sheets-Sheet 2 1 2 a s a United States Patent 4 Claims. (for. 3ss 22 My invention relates to temperature-responsive current control devices and, in a more particular aspect, to devices in which a thermistor of semiconductor material having a pronounced dependence of its resistance on magnetic fields, is provided with means for adjusting the thermistor resistance for a given temperature with the aid of a magnetic field.

Thermistors are electrical resistors which exhibit a higher ohmic resistance at lower temperature than at higher temperature. In known thermistors, the resistance-temperature characteristic is substantially fixed. That is, it can be changed only by mechanical means such as changing solder connections or switching from one to another resistance tap by plugs or selected similar electrical contact devices.

It is an object of my invention to provide a thermistor device whose resistance for a given temperature can be adjusted in a simpler manner. Another object of the invention is to provide a thermistor device with means that afford a continuous control of the resistance relative to a given temperature.

To this end, and in accordance with my invention, I provide a temperature-responsive current control device with a thermistor for connection in a circuit whose current is to be thermally controlled, the thermistor being formed of galvanomagnetic semiconductor resistance material, and I further provide variable magnetic means having a field in which the semiconducting thermistor is located for magnetically adjusting the thermistor resistance with respect to a given temperature.

According to another feature of my invention, the semiconductor material of the thermistor in the described device is doped to a conductance at which the relative change of resistance in the magnetic field is virtually independent of the temperature.

It is known that certain semiconductor resistance materials are controllable magnetically and hence Without mechanical contacts. When such a semiconductor resistor is subjected to a magnetic field having a magnetic induction B, the semiconductor resistance R can be expressed by the following equation:

In this equation a denotes the electron mobility of the semiconductor material of which the galvanomagnetic resistor is formed. The term R denotes the resistance of the galvan-omagnetic resistor when the magnetic induction B=(), that is, when the magnetic field is absent. Consequently, the temperature dependence of the resistance R is determined by the temperature dependence of the zero-field resistance R and by the temperature dependence of the function f(/L B) and hence the electron mobility ,u Generally, therefore, the temperature dependence of R in semiconductor resistors is also a function of f( B).

By suitable doping, a semiconductor member operating as a thermistor, can be given such a conductance that the relative change of the resistance in the magnetic field is virtually independent of the temperature. This eifect can be achieved particularly when using semiconductor A B 3,281,749 Patented Oct. 25, 1966 compounds, preferably indium antimonide (InSb) or indium arsenide (InAs). A doping substance suitable for obtaining the just mentioned independence of the resistance change is zinc particularly.

By thus providing the magnetically controllable device with a semi-conducting thermistor material doped for a temperature-independent change of resistance in the magnetic field, the effective resistance of the device can be magnetically controlled so as to have a desired value for a given temperature, without requiring a change in terminal connections or other mechanical means, while securing an operational characteristic in which the temperature response of the resistance possesses the same value for any chosen value of magnetic induction B. In other words, by means of the magnetic field the resistance of the thermistor can be varied within available limits and in a continuous manner, if desired, without appreciably changing the dependence of the resistance upon changes in temperature.

In order that the present invention may be readily carried into effect, it will now be described with reference to the accompanying drawings, in which:

FIG. 1 is a schematic diagram of an embodiment of a temperature-responsive current control device circuit of the present invention; 7

FIG. 2 is a front view of another embodiment of a device of the present invention;

FIG. 3 is a side View of the embodiment of FIG. 2; and

FIGS. 4 and 5 are explanatory graphs showing measuring results obtained with a device of the present invention.

In FIG. 1, a load 11 is energized by electric current which is supplied at terminals 12 and passes through a control rheostat 13. The control rheostat 13 has an adjustable tap 14 which is controlled by a relay device 15. The relay device 15 is energized from an auxiliary current source 16 through a thermistor 17.

The thermistor 17 comprises a field plate, namely an elongated resistance body, preferably supported by a suitable substrate and formed of indium antimonide, for example. The thermistor 17 is mounted close to the load 11 so that it is subjected to the heat generated in the load 11 by the electric current. When the temperature increases excessively, the thermistor 17 reduces its resistance 50 that no current energizes the relay device 15. This increases the resistance of the control rheostat 13, thereby reducing the load current and lowering the temperature of the load 11.

The thermistor 17 is also mounted between the pole shoes of a magnetizable core 18, shown in section in FIG. 1. The excitation Winding 19 of the magnetizable core 18 is connected to a current source 21 through a control resistor 22. The resistor 22 permits the variation of the ampere turns of excitation, thus setting a datum value for the resistance of the thermistor 17 with respect to a given temperature.

In the embodiment of FIGS. 2 and 3, a thermistor 26 mounted on a rigid substrate 27 is displaceable between the pole shoes 28 and 29 of a magnetic structure 31 which is excited by a permanent magnet 32. The substrate 27 with the thermistor 26 is displaceable so as to extend more or less into the effective magnetic field of the magnet. The thermistor 26, consisting of a thin semiconductor layer on the substrate plate 27, is positioned in a plane in which the magnetic lines of force pass perpendicularly through the semi-conductor layer. A plurality of needle-shaped inclusions on silver strips 33 of the thermistor 26 are positioned perpendicular to both the direction of the magnetic field and the direction of current flow between terminals 34 and 35.

It will be understood that although in FIG. 1 the thermistor device is shown thermally coupled with an electric load to be controlled, the heating of the thermistor may be effected in any other manner and for various other purposes in accordance with the known diversity of uses to which therrnistors, generally, have been put.

FIGS. 4 and 5 represent curves obtained for measuring results made with an embodiment in which the thermistor proper was subjected to the field of an electromagnet whose field strength was varied substantially in the manner shown for magnet 18 in FIG. 1. The embodiment of the thermistor used in the tests was equipped with an InSb thermistor doped with zinc to exhibit a conductance of approximately 100 (ohm-cm.)* Measure ments were taken at different temperatures and different magnetic fields.

Indium antimonide doped with zinc has a conductance equal to 100 (ohm-cm.)- if the material contains 10 zinc atoms per cm. This corresponds to a concentration of 1.9 times 10" percent zinc in indium antimonide.

FIG. 4 indicates as the ordinate the resistance R, in ohms, of one of the galvanomagnetic thermistors, as a function of the temperature T, indicated as the abscissa in C. The curves 1 to 6 are the result of measurements made when the thermistor was subjected to magnetic fields of 0, 2, 4, 6, 8 and kilogauss (kg.), respectively, the magnetic field values being indicated in FIG. 4 for each of the respective curves. As explained above, a thermistor is supposed to satisfy the require ment that the relative change of its resistance in the magnetic field is largely independent of the temperature. For example, if one designates the resistance, as at T=20 C., by R and the resistance at T =50 C. by R then the ratio of R /R must remain virtually the same for all of the six curves. In fact, it follows from FIG. 4 that this ratio for B=l0, 8, 6, 4, 2 and 0 kg. in the same sequence was R /R =0.38, 0.34, 0.32, 0.3, 0.3 and 0.33.

FIG. 5 shows the measuring results ascertained at different temperatures with an embodiment of the abovedescribed InSb semiconductor doped with zinc to a conductance of approximately 100 (ohm-cm.) The ordinate indicates the relative specific resistance AS/S percent as a function of the magnetic field B acting upon the thermistor, the field being plotted along the abscissa in kg. In the magnetic field B, the amout A9 constitutes the excess of a specific resistance above the specific resistance 3 existing when no magnetic field is applied. Curve 7 was taken at a temperature T:15.2 C. curve 8 at -T=25.0 C., curve 9 at T=37.5 C., and curve 10 at T=56.0 C.

All four curves of FIG. 5 are so close to each other that the relative change of the thermistor resistance as a function of the magnetic field is independent of the temperature in the range of the temperatures or temperature variations occurring in practice. In the embodiment whose measuring results are represented in FIG. 5, the temperature dependence between 0 and 10,000 gauss is approximately 2% per degree. For increasing the magnetically responsive change in thermistor resistance, it is often advisable to provide the surface of the thermistor body with parallel strips 33 of good conducting material, preferably silver or indium. The strips 33 are schematically shown on the thermistor 26 in FIG. 3. The strips 33 should, extend transverse to the direction of current flow between the terminals 34 and 35 of the thermistor (FIG. 3) and should also be positioned in planes perpendicular to the direction of the magnetic field. The strips 33 are in accordance with those more fully described and explained in US. Patent 2,894,234 of H. Weiss and H. Welker, assigned to the assignee of the present invention.

A similar improvement in response to magnetic fields is obtained by providing the semiconductor material with .electrically good conducting inclusions, preferably needle- .4 shaped inclusions of nickel antimonide in a semiconductor body of indium antimonide, the inclusions being oriented parallel to each other and preferably directed in the manner explained above with reference to the surface strips 33. A semiconductor body with such inclusions is produced for example by melting indium antimonide together with 1.8% by weight of nickel antimonide. The melt thus formed has a eutectic composition. During the cooling of the melt, the needle-shaped inclusions of nickel antimonide segregate as a second phase out of the embedding indium antimonide as substance because they are not soluble in InSb in the solid state. By applying normal freezing during the solidifying stage or by subsequently subjecting the ingot to zone melting, the inclusions are oriented in the above-described manner. Such and various other inclusions of different materials, as well as their provision in other galvanomagnetic semiconductor materials are more fully described in the copending application of H. Weiss and M. Wilhelm, Serial No. 273,776, filed April 17, 1963, and assigned to the assignee of the present invention.

While the invention has been described by means of specific examples and in specific embodiments, I do not wish to be limited thereto, for obvious modifications will occur to those skilled in the art without departing from the spirit and scope of the invention.

I claim:

1. A temperature-responsive current control device, comprising a thermistor having terminals for connection in a circuit whose current is to be thermally controlled, said thermistor comprising galvanomagnetic semicon ductor resistance material and having an electrical resistance which varies with temperature in a determined relationship, and variable magnetic means providing a field in which said thermistor is located for magnetically adjusting the electrical resistance of said thermistor at a given temperature.

2. A temperature-responsive device as claimed in claim 1, wherein said thermistor is formed substantially of semiconductor material from the group consisting of indium arsenide and indium antimonide and is doped with zinc, said thermistor having a rate of temperature-responsive change substantially independent of the magnetic induction in said field.

3. A temperature-responsive device as claimed in claim 1, said thermistor being formed of indium antimonide and having a multiplicity of elongated strips of metallic conductance extending on the thermistor surface parallel to each other and transverse to the direction of current flow through said thermistor.

4. A temperature-responsive device as claimed in claim 1, said thermistor being formed of indium antimonide and having a multiplicity. of needle-shaped inclusions of nickel antimonide embedded and dispersed in the indium antimonide and extending transverse to the direction of current flow through said thermistor.

References Cited by the Examiner UNITED STATES PATENTS 2,736,858 2/1956 Welker 33832 X 2,778,802 1/1957 Willardson et al. 1481.5 X 2,858,275 10/1958 Folberth --134 X 2,894,234 7/1959 Weiss et al. 317-234 X 2,924,633 2/ 1960 Sichling et al. 338-32 X FOREIGN PATENTS 863,104 3/ 1961 Great Britain.

1,001,378 1/1957 Germany.

1,066,268 10/ 1959 Germany.

1,069,755 11/ 1959 Germany.

RICHARD M. WOOD, Primary Examiner.

W. D. BROOKS, Assistant Examiner. 

1. A TEMPERATURE-RESPONSIVE CURRENT CONTROL DEVICE, COMPRISING A THERMISTOR HAVING TERMINALS FOR CONNECTION IN A CIRCUIT WHOSE CURRENT IS TO BE THERMALLY CONTROLLED, SAID THERMISTOR COMPRISING GALVANOMAGNETIC SEMICONDUCTOR RESISTANCE MATERIAL AND HAVING AN ELECTRICAL RESISTANCE WHICH VARIES WITH TEMPERATURE IN A DETERMINED RELATIONSHIP, AND VARIABLE MAGNETIC MEANS PROVIDING A FIELD IN WHICH SAID THERMINSTOR IS LOCATED FOR MAGNETICALLY ADJUSTING THE ELECTRICAL RESISTANCE OF SAID THERMISTOR AT A GIVEN TEMPERATURE. 